Determination of Initial Transmit Power Based on Shared Transmit-Power Information

ABSTRACT

Methods and systems are disclosed herein that may be used to share transmit-power information between mobile stations. An exemplary method involves a first mobile station: (i) determining a verified transmit power (VTP) for the first mobile station; (ii) using the VTP to generate a transmit-power message, wherein the transmit-power message is usable to determine an initial transmit power (ITP) for the second mobile station; and (iii) the first mobile station sending the transmit-power message to at least the second mobile station. For instance, the first mobile station may set the ITP for the second mobile station equal to the VTP for the first mobile station, and include an indication of the ITP in the transmit-power message. Alternatively, the first mobile station may calculate the ITP for the second mobile station by adjusting its VTP according to the ratio of the distance between the second mobile station and the serving base station, and the distance between the first mobile station and the serving base station.

BACKGROUND

Many people use mobile stations, such as cell phones and personaldigital assistants (PDAs), to communicate with cellular wirelessnetworks. These mobile stations and networks typically communicate witheach other over a radio frequency (RF) air interface according to awireless protocol such as Code Division Multiple Access (CDMA), perhapsin conformance with one or more industry specifications such as IS-95and IS-2000. Wireless networks that operate according to thesespecifications are often referred to as “1xRTT networks” (or “1xnetworks” for short), which stands for “Single Carrier RadioTransmission Technology.” Another CDMA protocol that may be used isknown as Evolution Data Optimized (EV-DO), perhaps in conformance withone or more industry specifications such as IS-856, Rel. 0 and IS-856,Rev. A. Other protocols may be used as well, such as Global System forMobile Communications (GSM), Time Division Multiple Access (TDMA),WiMax, and/or any others.

These networks typically provide services such as voice, Short MessageService (SMS) messaging, and packet-data communication, among others,and typically include a plurality of base stations, each of whichprovide one or more coverage areas, such as cells and sectors. Thesebase stations are typically not associated with any subscriber or smallgroup of subscribers in particular; rather, they are placed inpublicly-accessible locations and are used by the service provider'scustomers generally, and their coverage areas collectively blanketcities, rural areas, etc. When a mobile station is positioned in one ofthese coverage areas, it can communicate over the air interface with thebase station, and in turn over one or more circuit-switched and/orpacket-switched signaling and/or transport networks to which the basestation provides access. In such an arrangement, thebase-station-to-mobile-station link is known as the forward link, whilethe mobile-station-to-base-station link is known as the reverse link.

When a mobile station seeks to, as examples, originate a communicationsession (e.g. a voice call) or respond to a page message from a basestation, the mobile station sends one or more messages known as accessprobes to the base station over a reverse-link access channel. As partof this process, the mobile station determines a transmit power level atwhich to send communications to the base station.

More specifically, to arrive at an appropriate transmit power forcommunications, a mobile station typically determines an initialtransmit power at which to send an initial access probe, and thentransmits an access probe at the initial transmit power. If the basestation does not acknowledge the initial access probe, the mobilestation then re-transmits the access probe at an incrementally higherpower level (e.g. 3 dB higher than the previous access probe). Themobile station repeats this process (i.e. incrementally increasing thepower level and re-transmitting) until either receiving anacknowledgement from the base station or reaching a set number (e.g.five) of transmitted access probes. The mobile station may then wait atimeout period, and start again at the initial transmit power. Themobile station may repeat this entire cycle a set number of times (e.g.three) before concluding that the base station is not reachable, orperhaps waiting a longer timeout period before starting the entiresequence over. And other variations on this access-probe-sendingsequence exist as well, as this description is merely an example.

OVERVIEW

In current implementations, the initial transmit power is typicallydetermined by summing a set of values, all of which pertain toforward-link conditions and pilot-signal strength. For example, whenpreparing to send an access probe, a mobile station may sum (i) a valuethat reflects the power at which the mobile station is receivingtransmissions from the base station on the forward link, (ii) one ormore constants, and (iii) an interference-correction factor that isderived from the signal-to-noise ratio at which the mobile station iscurrently receiving a pilot signal from the base station.

There are drawbacks to the existing techniques for determining theinitial transmit power. For instance, while access probes aretransmitted over the reverse link access channel, the initial transmitpower is calculated based on forward link parameters, relying on theassumption that conditions on the forward link and the reverse link aresimilar. In practice, however, reverse link conditions may differ fromthose on the forward link, and resulting inaccuracies may lead toinefficient use of reverse-link resources. For example, some mobilestations may transmit access probes with more power than is required toreach the base station. And repeated attempts to transmit an accessprobe, which occur when the calculated initial transmit power is toolow, also increase congestion on the reverse-link. This effect may beamplified the more inaccurate a calculation is, as more attempts totransmit the access probe may be required before the access probesuccessfully reaches the base station.

Accordingly, exemplary methods and systems are described herein that mayhelp improve the accuracy with which mobile stations determine theinitial transmit power for an access probe, which in turn may result inmore efficient utilization of reverse-link resources and/or a reductionin the number of access-probe transmission attempts, among otherbenefits. To do so, when a mobile station successfully connects anddetermines a transmit power for its communications, the mobile stationmay share this “verified” transmit power (VTP) with, or use its VTP todetermine the initial transmit power for, nearby mobile stations. Sincethe verified transmit power accounts for actual reverse-link conditionsin the coverage area, using the verified transmit power of anothermobile station in the same coverage area may help a mobile station tocalculate an initial transmit power that is more accurate (i.e., that iscloser to the verified transmit power that the mobile station ultimatelydetermines).

In one aspect, an exemplary method involves (i) at a first mobilestation configured to operate in a radio access network, determining averified transmit power (VTP) for the first mobile station; (ii) thefirst mobile station using the VTP to generate a transmit-power message,wherein the transmit-power message is usable to determine an initialtransmit power (ITP) for the second mobile station; and (iii) the firstmobile station sending the transmit-power message to at least the secondmobile station.

In an exemplary embodiment, the step of using the VTP to generate atransmit-power message may involve using the VTP for the first mobilestation as a basis for determining the ITP for use by the second mobilestation, and the transmit-power message may therefore include anindication of the ITP for use by a second mobile station. In one suchembodiment, determining the ITP for the second mobile station based onthe VTP may involve setting the ITP for use by the second mobile stationequal to the VTP. In other such embodiments, determining the ITP for thesecond mobile station based on the VTP may involve using (i) the VTP forthe first mobile station, (ii) location information for the first mobilestation, and (iii) location information for the second mobile station asa basis for determining the ITP for the second mobile station. Forexample, the first mobile station may (i) determine a first distancebetween the first mobile station and the base station; (ii) determine asecond distance between the second mobile station and the base station;and (iii) use the ratio between the second distance and the firstdistance and the VTP for the first mobile station as basis fordetermining the ITP for the second mobile station (e.g., such as byweighting the VTP by the ratio between the second distance and the firstdistance).

Alternatively, the step of using the VTP to generate a transmit-powermessage may involve including an indication of the VTP (and possibly anindication of the location of the first mobile station as well) in thetransmit-power message. A second mobile station that receives thetransmit-power message can thereby use the VTP for the first mobilestation as a basis for determining its ITP.

In a further aspect, another exemplary method involves (i) at a secondmobile station configured to operate in a radio access network,receiving a transmit-power message that was transmitted from a firstmobile station; (ii) the second mobile station using the transmit-powermessage as a basis for determining an initial transmit power (ITP); and(iii) the second mobile station transmitting an access probe at the ITP.

And in a further aspect, a system is disclosed, which includes: (i) datastorage; (ii) at least one processor; and (iii) program logic stored inthe data storage and executable by the at least one processor to: (a)cause a second mobile station to receive a transmit-power message thatwas transmitted by a first mobile station; (b) use the transmit-powermessage as a basis to determine an initial transmit power (ITP) for thesecond mobile station; and (c) cause the second mobile station totransmit an access probe at the determined ITP.

And in yet a further aspect, another system is disclosed, whichincludes: (i) data storage; (ii) at least one processor; and (iii)program logic stored in the data storage and executable by the at leastone processor to: (a) determine a verified transmit power (VTP) for afirst mobile station; (b) use the VTP as a basis to generate atransmit-power message, wherein the transmit-power message is usable bya second mobile station to determine an initial transmit power (ITP) forthe second mobile station; and (c) cause the first mobile station tosend the transmit-power message to at least the second mobile station.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is described hereinwith reference to the drawings, in which:

FIG. 1 is a simplified block diagram of a wireless communication systemin which an exemplary system and method may be implemented;

FIG. 2 is a block diagram illustrating a system according to anexemplary embodiment;

FIG. 3 is a flow chart illustrating a method according to an exemplaryembodiment;

FIG. 4 is another flow chart illustrating a method according to anexemplary embodiment;

FIG. 5 is another flow chart illustrating a method according to anexemplary embodiment;

FIG. 6 is a flow chart illustrating a method in which the functionalityof determining initial transmit power is shifted to the second mobilestation that receives a transmit-power message from the first mobilestation, according to an exemplary embodiment; and

FIG. 7 is another flow chart illustrating a method in which thefunctionality of determining initial transmit power is shifted to thesecond mobile station that receives a transmit-power message from thefirst mobile station, according to an exemplary embodiment.

DETAILED DESCRIPTION I. Exemplary Network Infrastructure

Exemplary embodiments of the present invention are described herein. Itshould be understood that the word “exemplary” is used herein to mean“serving as an example, instance, or illustration.” Any embodimentdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments. Further, those skilledin the art will understand that changes and modifications may be made tothese embodiments without departing from the true scope and spirit ofthe invention, which is defined by the claims.

Referring to the drawings, FIG. 1 is a simplified block diagram of awireless communication system in which an exemplary method and systemmay be implemented. In such a wireless communication system, a wirelesscarrier typically operates a radio access network (RAN) 102, which iscontrolled by a switching entity such as a mobile switching center (MSC)104. The MSC generally includes or connects with one or more basestation controllers (BSCs) 106, which in turn connect with one or morebase transceiver stations (BTSs) 108. Each BTS 108 conventionallyincludes a cell tower with one or more antennas that communicate withmobile stations 112, 113, 115 via air interfaces 110.

Communications between the RAN 102 and mobile stations 112, 113, 115 mayoccur in accordance with any air interface protocol now known or laterdeveloped. Examples of such protocols include CDMA (e.g., 1xRTT,1xEV-DO), iDEN, TDMA, AMPS, GSM, GPRS, UMTS, EDGE, WiMAX (e.g., IEEE802.16), LTE, microwave, satellite, MMDS, Wi-Fi (e.g., IEEE 802.11),Bluetooth, and infrared. Other protocols may also be employed.

With the illustrated configuration, RAN 102 may provide service in anarea that is divided geographically into a number of cells, each definedby a radio frequency (RF) radiation pattern from a BTS 108. Furthermore,each cell may be subdivided into a number of sectors. For simplicity,references to a “sector” herein should be understood to include sectors,cells, and possibly other types of coverage areas as well. In general,air interface communications in each sector (or other such coveragearea) of a cellular wireless communication system can be encoded orcarried in a manner that distinguishes the communications in that sectorfrom communications in adjacent sectors. For example, in a Code DivisionMultiple Access (CDMA) system, each sector has a respectivepseudo-random noise offset or “PN offset” that is used to encode ormodulate air interface communications in the sector distinctly fromthose in adjacent sectors. Analogously, in other air interfaceprotocols, communications in one sector may be distinguished from thosein other sectors by frequency, time, and/or various other parameters.

BTS 108 may be any network element arranged to carry out the BTSfunctions described herein. As such, BTS 108 may include a communicationinterface, a processor, and data storage comprising instructionsexecutable by the processor to carry out those BTS functions. Thecommunication interface may include one or more antennas, chipsets,and/or other components for providing one or more CDMA coverage areassuch as cells and sectors, for communicating with mobile stations suchas mobile station 112 over an air interface. The communication interfacemay also include one or more wired (e.g. Ethernet) and/or wireless (e.g.WiFi or WiMax) interfaces for communicating with at least BSC 106.

BSC 106 may be any network element arranged to carry out the BSCfunctions described herein. As such, BSC 106 may include a communicationinterface, a processor, and data storage comprising instructionsexecutable by the processor to carry out those BSC functions. Thecommunication interface may include one or more wired (e.g. Ethernet)and/or wireless (e.g. WiFi or WiMax) interfaces for communicating withat least BTS 108, and mobile switching center (MSC) 104. In general, BSC106 functions to control one or more BTSs such as BTS 104, and toprovide those one or more BTSs with connections to switches such as MSC104 or a packet data serving node (PDSN) 114, for instance.

Note that the combination of BTS 108 and BSC 106 may be considered abase station. However, BTS 108 or BSC 106 could, taken alone, each beconsidered a base station as well. Furthermore, a base station may beconsidered to be either or both of those devices, and perhaps make useof one or more functions provided by MSC 104, and/or other networkentities.

MSC 104 and PDSN 114 may be any networking elements arranged to carryout the switch functions described herein. Thus, MSC 104 and/or PDSN 114may include a communication interface, a processor, and data storagecomprising instructions executable by the processor to carry out thoseswitch functions. MSC 104 preferably functions to provide connectivityto a public-switched telephone network (PSTN) 116, while PDSN 114preferably functions to provide connectivity to one or morepacket-switched networks 118, such as the Internet. Accordingly, thecommunication interface of PDSN 114 may include one or more wired (e.g.Ethernet) and/or wireless (e.g. WiFi or WiMax) interfaces forcommunicating with at least BSC 106 and other entities viapacket-switched network 118. Further, it should be understood that whileMSC 104 and PDSN 114 are shown as separate entities, some or all of thefunctionality of these entities may be combined in a single switchingentity.

Mobile stations 112, 113, 115 may be any type of mobile device arrangedto carry out the mobile-station functions described herein. As examples,mobile station 112 could be a cell phone, a PDA, a computer, a laptopcomputer, a hybrid CDMA/EV-DO device, and/or a multi-mode cellular/Wi-Fidevice. As such, a mobile station may include a user interface, awireless-communication interface, a processor, and data storagecomprising instructions executable by the processor for carrying outthose mobile-station functions. The user interface may include buttons,a touchscreen, a microphone, and/or any other elements for receivinginputs, as well as a speaker, one or more displays, and/or any otherelements for communicating outputs. Further, while the term “mobilestation” is a term of art commonly used for such devices, the term“mobile station” should be understood to include non-mobile devices,such as a personal computer or any other device capable of thefunctionality of a mobile station described herein.

In another aspect, RAN 102 and mobile station 112 may be configured forOver-The-Air Service Provisioning (OTASP). OTASP allows serviceproviders to communicate with a mobile station using a wireless network,such as the Internet, in order to add new types of services to themobile station, rather than requiring that the customer to bring themobile station to a service provider location (e.g., a storefront orservice center) for reprogramming. Accordingly, mobile station 112 maybe configured with the functionality described herein using OTASP.

II. Exemplary Systems

FIG. 2 is a block diagram illustrating a system according to anexemplary embodiment. An exemplary system may take the form of a mobilestation, may be a component of a mobile station, or may be a standalonesystem in communication with a mobile station. For purposes of examplein FIG. 2, the exemplary system takes the form of a mobile station 200.By way of example, mobile station 200 could be a cell phone, wirelesslyequipped personal digital assistant (PDA), or any other type ofwirelessly-equipped device now known or later developed. Further, itshould be understood that while the term “mobile station” is a term ofart commonly used for devices that are capable of wirelesscommunications, the term “mobile station” should be understood toinclude non-mobile devices, such as a personal computer or any otherdevice capable of the functionality of a mobile station describedherein.

The mobile station 200 is preferably equipped with hardware, software,and/or other logic to communicate with a RAN in accordance with anagreed communication protocol, such as one of the protocols noted hereinfor instance. For example, mobile station 200 may include a radiofrequency (RF) communication interface 202 that functions to facilitateair interface communications with a RAN according to one or moreprotocols such as those noted above. More generally, the communicationinterface 202 may be able to communicate with one or more of varioustypes of networks and devices, such as EV-DO networks, Wi-Fi networks,Bluetooth devices, and/or one or more additional types of networks anddevices.

Mobile station 200 may also include program logic 204 stored in datastorage 206 (e.g., one or more volatile and/or non-volatile storagecomponents of the mobile station, such as magnetic, optical, or organicstorage components) and executable by one or more processors 208 (e.g.,general purpose and/or special purpose processors) to carry out thevarious mobile-station functions described herein. In general, theprocessor 208 and data storage 206 may be any suitable components knownto those of skill in the art.

Furthermore, mobile station 200 is preferably configured to determinelocation information that is indicative of its location. Accordingly,mobile station 200 may also include a GPS receiver 210. Further, mobilestation 200 may include program logic 204 that when executed byprocessor 208 can operate the GPS receiver 210 to receive GPS locationdata from one or more GPS satellites, which may be used to determine thelocation of the mobile station 200 (or may simply indicate the locationin and of itself). Accordingly, the wireless communication device mayutilize the World Geodetic System WGS84 coordinate system or any otherappropriate coordinate system, to specify its location.

Additionally or alternatively, mobile station 200 may include programlogic 204, or possibly a separate chipset, which is configured forlocation-determination techniques other than using GPS (possiblycombining such techniques with GPS). For example, mobile station 200 maybe configured to determine its location using techniques such asAdvanced Forward Link Trilateration (AFLT), Enhanced Forward LinkTriangulation (EFLT), Time Difference On Arrival (U-TDOA), CellIdentification (CID), Enhanced Cell Identification (E-CID), and/or Angleof Arrival (AOA), among others.

In a further aspect, mobile station 200 may be configured to determinethe transmit power at which it will communicate with a given basestation. To do so, mobile station 200 may determine an initial transmitpower (ITP) and initially send an access probe at the ITP. Then, if noacknowledgement is received, mobile station 200 may increase itstransmit power and retransmit the access probe until either anacknowledgment is received, or the attempt to connect is deemed to havefailed (e.g., after a certain number of attempts or a predeterminedtimeout period).

Mobile station 200 may be configured to determine its ITP using varioustechniques. For example, according to IS-2000, the mobile station usesthe mean input power (mean_input_pwr), a PCS correction(Correction_PCS), and an interference correction(Interference_Correction) to determine initial-access-probe power (IP).The interference correction is defined as:

Interference_Corr=min(max(−7−E _(c) /I _(O),0),7)).

Further, a nominal power parameter (Nom_Pwr), a nominal power extensionparameter (Nom_Pwr_Ext), and an Initial Power parameter (Init_Pwr) arealso provided to adjust the IP calculation. The PCS correction isdefined as:

Correction_PCS=Nom_Pwr−(16*Nom_Pwr_Ext)+Init_Pwr

Thus, under IS-2000, ITP is calculated in decibels (dB) as:

ITP=−(mean_input_pwr)−76+Correction_PCS+Interference_Corr=−(mean_input_pwr)−76+Nom_Pwr−(16*Nom_Pwr_Ext)+Init_Pwr+Interference_Corr

In practice, existing IS-2000 mobile stations typically use a ReceivedSignal Strength Indicator (RSSI) as the mean input power, and typicallyset Nom_Pwr_Ext to be equal to zero. Further, the initial powerparameter may also be referred to as the Probe Adjust Power(Probe_Pwr_Adj). Yet further, the interference correction may be basedon the interference experienced on the forward link (E_(C)/I_(O)), andthus may also be referred to as the E_(C)/I_(O) Correction (E_(C)/I_(O)_(—) Correction). As such, an IS-2000 mobile station may calculateinitial-access-probe power according to the following:

ITP=−(RSSI)−76+(Nom_Pwr)+Probe_Adj_Pwr+E_(C)/I_(O) _(—) Correction

In this equation, the RSSI is typically an indication of received signalstrength at the mobile station, as measured by the mobile station. TheNominal Power (Nom_Pwr) is typically a network setting that isdetermined by the BSC or another network entity and relayed to mobilestations via BTSs, which in practice is typically a constant value fromzero and three. Nom_Pwr is typically provided to a mobile station in apage message that is transmitted when the mobile station powers on, butmay be provided using other techniques as well. Probe_Adj_Pwr istypically a constant that is predefined by the service provider.

According to an exemplary embodiment, mobile station 200 is additionallyor alternatively configured to coordinate with other mobile stations todetermine its ITP and/or to assist other mobile stations in determiningtheir respective ITPs. In particular, once mobile station 200 hasdetermined a VTP for communication with a given base station (i.e., thetransmit power used when an acknowledgement is successfully receivedfrom the base station), this transmit power may be considered a“verified” transmit power (VTP) for mobile station 200. Mobile station200 may use the VTP to generate a transmit-power message, and then sendthe transmit-power message to other nearby mobile stations to providethese mobile stations with, or assist these mobile stations indetermining, their respective ITPs.

In an exemplary embodiment, mobile station 200 may use its VTP todetermine an ITP that should be used by a nearby mobile station, andthen include an indication of the ITP for use by the nearby mobilestation in the transmit-power message. For example, mobile station 200may determine that nearby mobile stations should use its VTP as thenearby mobile stations ITP, and thus set the ITP in the transmit-powermessage to be its VTP. This technique may be employed for mobilestations that are close enough (e.g., within range or within apredetermined distance (e.g., 100 ft,) of the mobile station), which maybe selected that using the VTP of mobile station 200 will likely be moreaccurate than using the standard IS-2000 technique or other techniquesfor calculating ITP. As another example, mobile station 200 may use: (i)the VTP for the first mobile station, (ii) location information for thefirst mobile station, and (iii) location information for the secondmobile station as a basis for determining the ITP for the second mobilestation to determine an ITP for a nearby mobile station. By doing so,mobile station 200 may determine the ITP for a nearby mobile station byweighting its VTP by the ratio of its distance to the base station ascompared to the nearby mobile station's distance to the base station.

In an alternative embodiment, mobile station 200 may include anindication of the VTP for mobile station 200, rather than of the ITP forthe nearby mobile station. In such embodiments, the functionality ofdetermining the ITP for the nearby mobile station is moved from mobilestation 200, to the nearby mobile station. Further, in such embodiments,mobile station 200 may also determine its location, and include locationdata indicating its location in the transmit-power message. A nearbymobile station receiving the transmit-power message may then determineits ITP by comparing its distance to the base station to the distancebetween mobile station 200 and the base station, and adjusting thereceived VTP based on the relative distance to the base station.

To communicate transmit-power messages to other mobile stations, mobilestation 200 may be configured to communicate with other mobile stationsusing various protocols. Preferably, mobile station 200 uses Bluetooth,802.11, WiMAX or another such protocol that does not involve CDMAcommunications with the RAN, and preferably does not include the RAN inthe communication path with the other mobile station. As such, nearbymobile stations can receive the transmit-power message before connectingto the RAN. It should be understood, however, that in other scenarios,transmit-power messages may be communicated between mobile stations viathe RAN, without departing from the scope of the invention.

In a further aspect, mobile station 200 may also be configured toreceive transmit-power messages from other mobile stations, which eachmay provide an indication of the ITP to be used by mobile station 200,or an indication of the VTP for the other mobile station, and possiblylocation information for the other mobile station as well (from whichmobile station 200 can determine its own ITP). In the event the mobilestation 200 receives another mobile stations' VTP in a transmit-powermessage (rather than an instruction to use a specific ITP that has beencalculated for it), mobile station 200 may then determine its location,and use (i) the received indication of the VTP determined by the firstmobile station, (ii) the location information for the other mobilestation, and (iii) its location as a basis to determine the ITP at whichit should transmit an access probe.

As a specific example, the mobile station 200 may determine the distancebetween it and the serving base station (D₁), the distance between theother mobile station and the base station (D₂), and the ratio betweenthese distances (D₁/D₂). Mobile station 200 may then adjust the VTP ofthe other mobile station by this ratio in order to determine its ownITP, such as by multiplying the VTP by the ratio D₁/D₂. The mobilestation may then use the determined ITP as the starting point todetermine the transmit power for its communications with the basestation.

In an exemplary embodiment, mobile station 200 preferably uses ITPsdetermined for it by other nearby mobile stations or determines its ITPbased on VTPs of other mobile stations, rather than using a techniquesuch as that specified under IS-2000. Accordingly, in a further aspect,when mobile station 200 seeks to establish a connection with a basestation, the mobile station may first listen for a transmit-powermessage, which it can use to determine an ITP. If a transmit-powermessage is available from another mobile station being served by thebase station to which the mobile station is attempting to connect, thenmobile station 200 uses this transmit-power message to determine an ITPwith which to send an access probe. If, on the other hand, atransmit-power message is not available, then the mobile station may useanother technique, such as the IS-2000 technique, to determine an ITP.

In some embodiments, mobile station 200 may listen and/or search fortransmit-power messages on an as-needed basis, whenever the mobilestation is about to send an access probe. Alternatively, mobile station200 may routinely listen and/or search for transmit-power messagesindependent from a particular attempt to connect. By doing so, mobilestation 200 may update and store its ITP from time-to-time based onreceived transmit-power messages, so ITP value may be predetermined whenthe mobile station needs to send an access probe. As such, when mobilestation 200 needs to send an access probe, it may first check whether ithas determined and stored an ITP value (and possibly whether a storedITP is valid or expired). Then, if mobile station 200 has not alreadydetermined ITP (or the ITP is expired), mobile station 200 may searchfor a transmit-power message from another mobile station.

When mobile station 200 uses a VTP received from another mobile stationto determine its own ITP, and in turn uses its ITP to determine its ownVTP, mobile station 200 may then use its VTP to create and broadcast itsown transmit-power message to other nearby mobile stations.Alternatively or additionally, when mobile station 200 receives atransmit-power message, mobile station 200 may rebroadcast thetransmit-power message for nearby mobile stations (thus sharing anothermobile station transmit-power information with nearby mobile stations).In either case, by sharing transmit-power information between mobilestations, mobile station 200 and other nearby mobile stations cancoordinate to determine their respective ITPs, based solely oninformation provided by other mobile stations. Thus, in theory, it isonly necessary for a single mobile station in a given coverage area (orany other type of defined geographic area) to initially use IS-2000 oranother such technique to calculate ITP (of course, in practice, itshould be understood that this may not be the case). Since using sharedVTP information may result in ITP being more accurate, the overallnumber of access-probe transmission attempts may be reduced, which inturn may reduce usage of reverse-link resources for repeated accessprobe attempts.

III. Exemplary Methods

FIG. 3 is a flow chart illustrating a method 300 according to anexemplary embodiment. Method 300 is preferably carried out by a firstmobile station, or a system within or associated with a first mobilestation, in order to share transmit-power information with nearby mobilestations. As shown in block 302, the method involves the first mobilestation determining the verified transmit power (VTP) for the firstmobile station. The first mobile station then uses the VTP to generate atransmit-power message, which is usable to determine to determine theinitial transmit power (ITP) for a second mobile station, as shown byblock 304. The first mobile station then broadcasts the transmit-powermessage, as shown by block 306.

The step of using VTP to generate a transmit-power message, as shown inblock 304, may be implemented in various ways. For example, the firstmobile station may use its VTP as a basis for determining the ITP foruse by the second mobile station, and include an indication of thedetermined ITP in the transmit-power message. Alternatively, the firstmobile station may include an indication of its VTP in thetransmit-power message (possibly with location information indicatingits location as well), rather than an indication of ITP for the secondmobile station, thus transferring the functionality of determining theITP to the second mobile station, which receives the transmit-powermessage.

In embodiments where the first mobile station determines the ITP for thesecond mobile station, and includes an indication of the ITP in atransmit-power message, the ITP may be calculated using varioustechniques. As one example, the first mobile station may simply set theITP for the second mobile station equal to its own VTP. As anotherexample, the first mobile station may use: (i) the VTP for the firstmobile station, (ii) location information for the first mobile station,and (iii) location information for the second mobile station to adjustits VTP according to the ratio of the distance between the second mobilestation and the serving base station, and the first mobile station andthe serving base station.

FIG. 4 is another flow chart illustrating a method 400 according to anexemplary embodiment. Method 400 illustrates an embodiment where thefirst mobile station determines the ITP for a second mobile station byadjusting its VTP according to the ratio of the distance between thesecond mobile station and the serving base station, and the distancebetween the first mobile station and the serving base station.

As shown in block 402, method 400 involves the first mobile stationdetermining location information indicating the location of the firstmobile station. The first mobile station also determines its VTP, asshown by block 404. The VTP may be determined using an ITP calculatedaccording to IS-2000, an ITP calculated using transmit-power messagesfrom other mobile stations, or an ITP calculated using any otherappropriate technique. Additionally, the first mobile station receiveslocation information indicating the location of the second mobilestation, as shown by block 406. The location information for the secondmobile station is preferably provided to the first mobile station by thesecond mobile station using one of the variousmobile-station-to-mobile-station communication techniques describedherein. The first mobile station then uses (i) its VTP as determined inblock 404, (ii) the location of the second mobile station, and (iii) itslocation information as determined in block 402, in order to determinethe ITP that should be used by the second mobile station, as shown byblock 408. The first mobile station then sends a transmit-power messageto at least the second mobile station, as shown in block 410.

In an exemplary embodiment, to determine the ITP for the second mobilestation as shown in block 408, the first mobile station may use itslocation and the location of the serving base station to determine afirst distance (D_(MS1)) between the first mobile station and theserving base station. The first mobile station also uses the receivedlocation information for the second mobile station to calculate a seconddistance (D_(MS2)) between the second mobile station and the servingbase station. The first mobile station then determines the ratio of thesecond distance as compared to the first distance (D_(MS2)/D_(MS1)), andcalculates ITP for the second mobile station by weighting its VTP(VTP_(MS1)) by this ratio. For example, the first mobile station maycalculate ITP for the second mobile station (ITP_(MS2)) as:

ITP_(MS2)=(D _(MS2) /D _(MS1))*VTP_(MS1)

It should be understood that variations on this technique fordetermining ITP, which may incorporate other factors, are also possible.

FIG. 5 is another flow chart illustrating a method 500 according to anexemplary embodiment. Method 500 illustrates an embodiment where thefirst mobile station uses its VTP to determine the ITP for a secondmobile station, and includes an indication of that ITP in atransmit-power message. Further, in this embodiment, the first mobilestation uses one of two techniques to determine an ITP that should beused by a second mobile station (e.g., either setting the ITP equal toits own VTP, or using a method such as method 400 of FIG. 4), dependingupon the proximity of the second mobile station to the first mobilestation.

More specifically, in method 500, the first mobile station initiallyreceives location information (e.g., GPS coordinates) indicating thelocation of the second mobile station, as shown by block 502. The firstmobile station then makes a determination as to whether or not thesecond mobile station is within a predetermined distance from the firstmobile station, as shown by block 504. If the second mobile station iswithin the predetermined distance, then the first mobile station setsthe ITP for use by the second mobile station equal to the VTP, as shownby block 506. If, on the other hand, the second mobile station is notwithin the predetermined distance, then the first mobile station uses(i) the VTP for the first mobile station, (ii) the location of the firstmobile station, and (iii) the location of the second mobile station todetermine the ITP for the second mobile station, as shown in block 508.In either case, once ITP is determined, the first mobile stationbroadcasts a transmit-power message that includes an indication of theITP for the second mobile station, as shown by block 510. For example,the first mobile station may calculate ITP using a technique such asmethod 400 of FIG. 4.

Method 500 takes advantage of the recognition that two mobile stationsmay be located close enough to each other (e.g., within the broadcastrange or predetermined distance of each other), and experiencesimilar-enough reverse-link conditions, that the transmit power for bothmobile stations is likely to be similar. In this scenario, the VTPdetermined by the first mobile station is likely to be close to (orpossibly even the same as) the VTP that will ultimately determined bythe second mobile station. Thus, by setting the ITP for the secondmobile station to equal the VTP for the first mobile station, it ishoped that the ITP will be very close to (or possibly even equal to) theVTP that is ultimately determined by the second mobile station.Accordingly, where it is determined that the second mobile station isclose enough to the first mobile station, the first mobile station maysimplify the process of determining ITP for the second mobile station bysetting the ITP equal to its own VTP.

Setting the ITP for the second mobile station equal to the VTP of thefirst mobile station, such as in block 506, may also provide the benefitof determining the ITP for the second mobile station, independent of thelocation of the serving BTS. Specifically, the alternative technique ofweighting the VTP by the ratio of mobile-station distances to theserving base station involves determining the distances from each mobilestation to the BTS. The first mobile station may determine its distanceto the BTS by calculating round-trip delay to and from the BTS, or mayobtain the GPS coordinates of the BTS, and calculate the distancebetween its GPS coordinates and those of the BTS. For the second mobilestation, however, which is net yet connected to the BTS, round-tripdelay is not an option. Therefore, the first mobile station may use theGPS coordinates of the BTS, along with the GPS coordinates of the secondmobile station, to determine the distance between the second mobilestation and the BTS. This implementation may require a modification tosome existing BTSs to broadcast their GPS coordinates. Therefore,calculating the ITP for the second mobile station, without using theratio of mobile-station distances to the BTS, may avoid the need tomodify existing BTSs.

As noted, when the second mobile station is not close enough, anothertechnique may be used to determine the ITP for the second mobilestation, such as weighting the VTP by the ratio of the distances of themobile stations to the base station. Alternatively, when the secondmobile station is not within the predetermined distance from the firstmobile station, the first mobile station may send a transmit-powermessage indicating simply that the second mobile station should use astandard technique to determine its ITP, or that simply indicates thatthe first mobile station cannot provide an ITP for the second mobilestation. As another alternative, when the second mobile station is notwithin the predetermined distance, the first mobile station may simplyrefrain from transmitting a transmit-power message. In both cases, theneed to use the BTS's GPS coordinates to determine ITP may be eliminatedaltogether.

Furthermore, it should be understood that there is no definedrequirement for the distance at which a mobile station should beginusing the latter technique (e.g., using the locations of the mobilestation to determine the relative distances from the base station, andweighing VTP accordingly). However, there is a tradeoff between therange over which a given mobile station may use a simplified transmitpower message and the accuracy of using the VTP for the first mobilestation as an estimation of the VTP that will ultimately be determinedby the second mobile station. Accordingly, it is contemplated that thethreshold proximity of the first and second mobile stations to eachother may be selected as a matter of engineering design choice.

As noted, rather than determine the ITP for the second mobile station,the first mobile station may include an indication of its VTP (andpossibly an indication of its location) in a transmit-power message, andthe second mobile station receiving the message may then determine itsown ITP based on the VTP of the first mobile station. FIG. 6 is anotherflow chart illustrating a method 600 according to an exemplaryembodiment in which the functionality of determining the ITP is shiftedto the second mobile station that receives the transmit-power messagefrom the first mobile station. Method 600 is preferably carried out bythe first mobile station to send a transmit-power message including itsVTP to a second mobile station, which can be used by the second mobilestation to determine its ITP.

More specifically, as shown in block 602, method 600 involves the firstmobile station determining its own location. The first mobile stationalso determines a VTP for the first mobile station (i.e., theaccess-probe transmit power at which the first mobile receives anacknowledgement), as shown by block 604. The VTP may be determined usingan ITP calculated according to IS-2000, an ITP calculated usingtransmit-power messages from other mobile stations, or an ITP calculatedusing any other appropriate technique. The first mobile station thentransmits a transmit-power message, as shown in block 606. Thetransmit-power message preferably includes (i) an indication of the VTPand (ii) the determined location information for the first mobilestation. Accordingly, the transmit-power message is usable by a secondmobile station that receives the transmit-power message to determine ITPfor the second mobile station.

The first mobile station and/or the second mobile station may determinetheir respective locations using various techniques or combinations oftechniques. For example, each mobile station may simply determine itsGPS coordinates, use a triangulation-based method, or use an advancedtechnique such as AFLT, EFLT, U-TDOA, etc. In general, it should beunderstood that an exemplary method may involve any type oflocation-determination technique now known or yet to be discovered,without departing from the scope of the invention.

The first mobile station then includes its location information in atransmit-power message for nearby mobile stations. For example, theincluded location information may be GPS coordinates and/or otherinformation identifying the geographic location of the first mobilestation, which the second mobile station can use to determine thedistance between the first mobile station and the serving base station.Additionally or alternatively, the first mobile station may itselfcalculate its distance to the serving base station and include thisdistance in the transmit-power message.

The first mobile station may broadcast the transmit-power message sothat it is available to a second mobile station, or possibly to anymobile station, that is nearby. For example, the first mobile stationmay transmit the transmit-power message to some or all other mobilestations operating in the coverage area served by the same base stationthat is serving the first mobile station. This coverage area may be asector, a group of sectors served by a common base station, a subsectionof a sector, or an area defined in another manner. Alternatively, themobile station may broadcast the transmit-power message with apredetermined power, or a power level that is determined as a matter ofengineering design choice. Preferably, the transmit-power message isbroadcast or transmitted using a protocol formobile-station-to-mobile-station communication that does not involve theRAN in its communication path, such as Bluetooth, 802.11, etc. (Notethat herein, a “transmission” and a “broadcast” of a transmit-powermessage are considered to be interchangeable, both including instanceswhere the transmit-power message transmitted to a particular mobilestation or mobile stations, and instances where the transmit-powermessage is generally broadcast by a mobile station.)

FIG. 7 is another flow chart illustrating a method 700 according to anexemplary embodiment, in which the functionality of determining the ITPis shifted to the second mobile station receiving the transmit-powermessage. Method 700 is preferably carried out by the second mobilestation, or a system within or associated with the second mobilestation, in order to use shared transmit-power information received in atransmit-power message from a first mobile station, in order tocalculate its own ITP. Method 700 involves the second mobile stationreceiving a transmit-power message that was transmitted by a firstmobile station, as shown by block 702. The transmit-power messagepreferably includes an indication of a VTP determined by the firstmobile station (i.e., the VTP used by the first mobile station), andlocation information for the first mobile station. In addition, thesecond mobile station determines location information indicating itslocation, as shown by block 704. The second mobile station then uses:(i) the received indication of the VTP determined by the first mobilestation, (ii) the received location information for the first mobilestation, and (iii) the determined location information for the secondmobile station as a basis for determining an ITP with which to send anaccess probe, as shown by block 706. The method may further involve thesecond mobile station transmitting an access probe at the ITP for thesecond mobile station, as shown by block 708, to thereby begin theprocess of determining its own VTP.

Exemplary embodiments of the present invention have been describedabove. It should be understood the word “exemplary” is used herein tomean “serving as an example, instance, or illustration.” Any embodimentdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other embodiments. In addition, thoseskilled in the art will understand that changes and modifications may bemade to these exemplary embodiments without departing from the truescope and spirit of the invention, which is defined by the claims.

I claim:
 1. A method comprising: at a first mobile station configured tooperate in a radio access network, determining a verified transmit power(VTP) for the first mobile station; the first mobile station using theVTP to generate a transmit-power message, wherein the transmit-powermessage is usable to determine an initial transmit power (ITP) for thesecond mobile station; and the first mobile station sending thetransmit-power message to at least the second mobile station.
 2. Themethod of claim 1, wherein using the VTP to generate a transmit-powermessage comprises using the VTP for the first mobile station as a basisfor determining the ITP for use by the second mobile station, whereinthe transmit-power message comprises an indication of the ITP for use bya second mobile station.
 3. The method of claim 2, wherein using the VTPfor the first mobile station as a basis for determining the ITP for useby the second mobile station comprises setting the ITP for use by asecond mobile station equal to the VTP.
 4. The method of claim 2,wherein using the VTP for the first mobile station as a basis fordetermining the ITP for use by the second mobile station comprises using(i) the VTP for the first mobile station, (ii) location information forthe first mobile station, and (iii) location information for the secondmobile station as a basis for determining the ITP for the second mobilestation.
 5. The method of claim 4 wherein using (i) the VTP for thefirst mobile station, (ii) location information for the first mobilestation, and (iii) location information for the second mobile station asa basis for determining the ITP for the second mobile station comprises:determining a first distance between the first mobile station and thebase station; determining a second distance between the second mobilestation and the base station; and using (a) a ratio between the seconddistance and the first distance and (b) the VTP for the first mobilestation as basis for determining the ITP for the second mobile station.6. The method of claim 2, wherein using the VTP for the first mobilestation as a basis for determining the ITP for use by the second mobilestation comprises: making a determination as to whether or not thesecond mobile station is within a predetermined distance from the firstmobile station; if the determination is that the second mobile stationis within the predetermined distance, then setting the ITP for use by asecond mobile station equal to the VTP; and if the determination is thatthe second mobile station is not within the predetermined distance, thenusing (i) the VTP for the first mobile station, (ii) locationinformation for the first mobile station, and (iii) location informationfor the second mobile station as a basis for determining the ITP for thesecond mobile station.
 7. The method of claim 1, wherein thetransmit-power message comprises an indication of the VTP, and whereinthe indication of the VTP is usable by a second mobile station thatreceives the transmit-power message to determine the ITP for the secondmobile station.
 8. The method of claim 7, further comprising the firstmobile station determining location information for the first mobilestation, wherein the transmit-power message further comprises thedetermined location information for the first mobile station.
 9. Themethod of claim 1 wherein determining the VTP for the first mobilestation comprises: transmitting an access probe to a base station in theradio access network and waiting for an acknowledgement from the basestation, wherein transmit power of the access probe is initially set ata predetermined ITP; if the acknowledgement is not received from thebase station within the predetermined period of time, then repeatedly(i) increasing the transmit power, (ii) re-transmitting the access probeto the base station, and (iii) waiting the predetermined period of time,until the acknowledgement is received from the base station; anddetermining the VTP to be the transmit power of the access probe whenthe acknowledgement is received from the base station.
 10. A methodcomprising: at a second mobile station configured to operate in a radioaccess network, receiving a transmit-power message that was transmittedfrom a first mobile station, the second mobile station using thetransmit-power message as a basis for determining an initial transmitpower (ITP); and the second mobile station transmitting an access probeat the ITP.
 11. The method of claim 10, wherein the transmit-powermessage comprises an indication of the ITP.
 12. The method of claim 10,wherein the transmit-power message comprises an indication of a verifiedtransmit power (VTP) for the first mobile station, and wherein using thetransmit-power message as a basis for determining the ITP comprisesusing the received indication of the VTP for the first mobile station asa basis for determining the ITP.
 13. The method of claim 12, whereinusing the received indication of the VTP for the first mobile station asa basis for determining the ITP comprises the second mobile stationsetting the ITP equal to the VTP for the first mobile station.
 14. Themethod of claim 10, wherein the transmit-power message comprises (i) anindication of a VTP for the first mobile station and (ii) locationinformation for the first mobile station, the method further comprising:the second mobile station determining location information for thesecond mobile station; wherein using the transmit-power message as abasis for determining the ITP comprises using (i) the indication of theVTP for the first mobile station, (ii) the location information for thefirst mobile station, and (iii) the location information for the secondmobile station as a basis for determining the ITP.
 15. The method ofclaim 14, wherein determining location information for the second mobilestation comprises using trilateration as a basis to determine locationinformation.
 16. The method of claim 14, wherein determining the ITPcomprises: using the received location information for the first mobilestation as a basis for determining a first distance between the firstmobile station and a base station in the radio access network; using thedetermined location information for the second mobile station as a basisfor determining a second distance between the second mobile station anda base station in the radio access network; and using (i) a ratiobetween the second distance and the first distance and (ii) the VTPdetermined by the first mobile station, as basis for determining the ITPfor the second mobile station.
 17. The method of claim 14, wherein thereceived location information for the second mobile station comprises afirst distance between the first mobile station and a base station inthe radio access network; wherein determining the location informationfor the second mobile station comprises determining a second distancebetween the second mobile station and a base station in the radio accessnetwork; and wherein determining the ITP for the second mobile stationcomprises using (i) a ratio between the second distance and the firstdistance and (ii) the VTP determined by the first mobile station, asbasis for determining the ITP for the second mobile station.
 18. Themethod of claim 10, further comprising: making an initial determinationthat the ITP for the second mobile station has not yet been determined;and in response to the initial determination, listening for thetransmit-power message.
 19. The method of claim 18, further comprising,if a transmit-power message is not received within a predeterminedperiod of time, using a predetermined ITP to send the access probe. 20.A system comprising: data storage; at least one processor; and programlogic stored in the data storage and executable by the at least oneprocessor to: (a) cause a second mobile station to receive atransmit-power message that was transmitted by a first mobile station;(b) use the transmit-power message as a basis to determine an initialtransmit power (ITP) for the second mobile station; and (c) cause thesecond mobile station to transmit an access probe at the determined ITP.21. The system of claim 20, wherein transmit-power message an indicationof the ITP for the second mobile station as determined by the firstmobile station.
 22. The system of claim 20: wherein the receivedtransmit-power message comprises (i) an indication of a verifiedtransmit power (VTP) for the first mobile station and (ii) locationinformation for the first mobile station; wherein the program logicstored in the data storage and executable by the at least one processorfurther comprises program logic stored in the data storage andexecutable by the at least one processor to: (a) determine locationinformation for the second mobile station; and (b) use the indication ofthe VTP for the first mobile station, the location information for thefirst mobile station, and the location information for the second mobilestation as a basis to determine the ITP for the second mobile station.23. The system of claim 22, wherein the program logic stored in the datastorage and executable by the at least one processor to determine theITP for the second mobile station comprises program logic stored in thedata storage and executable by the at least one processor to: use thereceived location information for the first mobile station as a basis todetermine a first distance between the first mobile station and a basestation in the radio access network; use the determined locationinformation for the second mobile station as a basis to determine asecond distance between the second mobile station and a base station inthe radio access network; and use (i) a ratio between the seconddistance and the first distance and (ii) the VTP determined by the firstmobile station, as basis to determine the ITP for the second mobilestation.
 24. The system of claim 22, wherein the received locationinformation for the second mobile station comprises a first distancebetween the first mobile station and a base station in the radio accessnetwork; wherein the program logic stored in the data storage andexecutable by the at least one processor to determine the ITP for thesecond mobile station comprises program logic stored in the data storageand executable by the at least one processor to: determine a seconddistance between the second mobile station and a base station in theradio access network; and wherein the program logic stored in the datastorage and executable by the at least one processor to determine theITP for the second mobile station comprises program logic stored in thedata storage and executable by the at least one processor to: use (i) aratio between the second distance and the first distance and (ii) theVTP determined by the first mobile station, as basis for determining theITP for the second mobile station.
 25. The system of claim 20, furthercomprising program logic stored in the data storage and executable bythe at least one processor to: based at least in part on thetransmission of the access probe at the determined ITP, determine a VTPfor the second mobile station; use the VTP for the second mobile stationas a basis to generate a second transmit-power message, wherein thesecond transmit-power message is usable by a third mobile station thatreceives the transmit-power message to determine an ITP for the thirdmobile station; and cause the second mobile station to broadcast thesecond transmit-power message.
 26. A system comprising: data storage; atleast one processor; and program logic stored in the data storage andexecutable by the at least one processor to: (a) determine a verifiedtransmit power (VTP) for a first mobile station; (b) use the VTP as abasis to generate a transmit-power message, wherein the transmit-powermessage is usable by a second mobile station to determine an initialtransmit power (ITP) for the second mobile station; and (c) cause thefirst mobile station to send the transmit-power message to at least thesecond mobile station.
 27. The system of claim 26, further comprisingprogram logic stored in the data storage and executable by the at leastone processor to use the VTP to determine the ITP for use by the secondmobile station, wherein the transmit-power message comprises anindication of the determined ITP for use by a second mobile station. 28.The system of claim 26, wherein the program logic stored in the datastorage and executable by the at least one processor to use the VTP todetermine the ITP for use by the second mobile station comprises:program logic stored in the data storage and executable by the at leastone processor to use (i) the VTP for the first mobile station, (ii)location information for the first mobile station, and (iii) locationinformation for the second mobile station as a basis to determine theITP for the second mobile station.
 29. The system of claim 26, whereinthe transmit-power message comprises an indication of the VTP, andwherein the indication of the VTP is usable by a second mobile stationthat receives the transmit-power message to determine the ITP for thesecond mobile station.
 30. The system of claim 29, further comprisingfurther comprising program logic stored in the data storage andexecutable by the at least one processor to determine locationinformation for the first mobile station, wherein the transmit-powermessage further comprises the determined location information for thefirst mobile station.